Trackball



FIG. 1 is the perspective view of a design for trackball showing my design;

FIG. 2 is the front elevational view thereof;

FIG. 3 is the rear elevational view thereof;

FIG. 4 is the left side elevational view thereof;

FIG. 5 is the right side elevational view thereof;

FIG. 6 is a top plan view thereof; and,

FIG. 7 is a bottom plan view thereof. 

The ornamental design for a trackball, as shown and described. 